A clock signal generation device applied to a mobile communication terminal has been used, in which, even if the reference frequency is shifted due to aging variation, by overwriting to update the initial parameter table with a parameter at the time of convergence by feedback control, or more specifically, a parameter corresponding to the reference frequency following the transmission frequency of the base station, even during the initial oscillation period at the next start-up, the reference frequency that follows the transmission frequency of the base station from the start is obtained (see, for example, Patent document 1). For example, in a mobile phone system using 800 MHz band, the following precision of a mobile communication terminal to the base station is required to be smaller than 1.5 ppm, and the precision must be smaller than 2 ppm in 1.5 GHz band mobile phone system.
In the meantime, the precision of ±0.05 ppm is required for the oscillating frequency of clock signal generation devices applied to wireless base stations for W-CDMA (wideband code division multiple access) for example, as described in Non-patent document 1 in 3GPP TS (3rd Generation Partnership Project Technical Specification) being a third-generation mobile phone standard.    [Patent document 1]: Japanese Laid-open Patent Publication 077670/2001 (paragraphs 0013 through 0020, and FIG. 1 and FIG. 3)    [Patent document 2]: Japanese Laid-Open Patent Publication 509346/1996    [Non-patent document 1]: 3GPP TS 25.141 (6.3 Frequency Error)    [Non-patent document 2]: 3GPP TS 25.427 (Node Synchronization)    [Non-patent document 3]: 3GPP TS 25.435 (Node Synchronization)